Long distance travel overseas

I'm looking for some help and advice. I'm moving to a different country and I have 2 rescue cats that I adopted whilst in my present home. I've searched the forums and seen some advice but don't think I can apply it to my situation.

My journey time according to google maps is 10 and a half hours which doesn't account for any stops or hanging around for Eurotunnel check in. I was originally going to go by ferry but have heard that cats hate ferries and they would have to stay on the car deck where it gets quite cold.

I've seen the advice about letting the cats out of their carriers in the car while it is stopped but this is not an option for me - my cats are rescues and I can't pick either one up so I would never get them back in their boxes. This means if the cats pee on the road I can't clean it up until I reach my destination. I also can't open the boxes to put food and water in. Will the cats be ok? How long before I leave should I feed them and take their water away to reduce the number of accidents?

I have some herbal medicine from the vet that should relax them on the journey and some Feliway. They don't like to travel so is there anything else I can do to calm them?

One final question - has anyone on here taken a cat through the pet check in at Eurotunnel. Is the building secure? I'm really worried about having to open the carrier to scan the microchip.

Is there anything I haven't even thought to ask?

Thank you for any help you can give - I'm really worried about this.

I am in the U.S. so cannot help you with info about the Eurotunnel building, but if you buy the kind of carrier that can be opened from the top as well as the front, it shouldn't be too hard for someone to slip a scanner in and scan the microchip without letting the cat get out.  I do know that some airlines in this country have a separate room with a door that closes that they use for more thorough security checking when needed, so if there is any way you can take the cats in their carriers to a room that can be completely closed, that would be best, even while you are trying to make sure they don't get out of the carrier. 

I traveled with cats, on a journey that took two days, driving 12 hours each day.  I had clip on water dishes with just a tiny bit of water in them in the carriers but no food dishes, and I doubt they drank anyhow.  I used incontinence pads in the boxes in case they had an accident, but they never did.  They used the box just before we left both days and just slept the entire trip after the first half hour or so.  I had catnip in the carriers also.  I have had cats poop in their carriers before, but not on that trip, and I traveled with 8 cats, 2 per carrier.  The incontinence pads (human size) are great because in case of a stinky accident, you can just fold them up and toss them and put in another one.  You might want to use TWO, one on top of another, since your cats are kind of on the feral side and it wouldn't be easy to insert a new pad.  Easier to just remove a soiled one and leave the second one in place.

My cat is usually calmed down with a towel wrapped around her
And let her explore IF she is curious enough but don't let her to
Close to the window of your car make sure to bring plenty of toys,
Treat,Cat food,blankets,and a bed to make sure your cats are as
Safe as possible!

Be sure to harness the cats and leash them - even if you need a Vet's help prior to leaving (same day). 10 or 11 hours is not a long journey. They will be fine. You have them in the plane with you, yes? (Not cargo?) If in passenger area you will have a soft carrier and won't be able to feed them. Try using homeopathic calmers such as Rescue Remedy Valerian or Melatonin before leaving. Spray the carriers and blankets with Feliway. Airlines require you to clean the crates if they poop, so the harnesses and leashes will help contain the cats if you need to reach in. 

If this seems overwhelming, hire pet courier help and they will transport in cabin to your new home. 

Thank you so much for the advice. I have some puppy training pads to put in the boxes but I hadn't thought of layering them so I could just remove the top one!

I'm not going by plane - it is car all the way - they stay in my car while I am on the train as well. I can't get a harness on either of them. One has a collar but the other got hers off and even with the vets help we couldn't get it back on so there is no way I'd get her in a harness!

Cats can hold their pee and their poop for a fairly long time, so long travel while it might cause them discomfort for a while. It isn't healthy for any human or animal to hold for a very long time.  I really would just stay away from anything that would cause them to feel and urge to go in the cage or whatever you bring them. A cat holding it for 10-12 hours is really okay unless the cat is over 12 years old then that would be the only time I wouldn't recommend doing it. For feeding just put them on dry food that you know works for them from now until you go on your long ride. Wet cat food I've found to not be a very good idea when you are going to be traveling with your cats/moving.  So at night give them a little bit more food then you would normally, and then in the morning you just give them each about 1/3 of what you normally give them. Just give them about a little bit less than what they would eat for dinner though when you take them on the long trip. Water is okay, just bring something so you can control their water intake. Like only give them 2oz of water every 2-3 hours. I did show cats a long long long time ago and this was always my setup for it. I would go 4-16 hours sometimes., and this was always my setup. Over feeding and having them on wet always would make them puke or have an accident. Just make sure you have the feeding and watering down and really you should be fine. Bring a rug or a blanket for the kennel and they should do great. cats and dogs can get really sick if they live inside something where they just went pee or poop for an extended amount of time. So it's healthier just to let them hold it.